1. Field of the Invention
The invention relates to a wireless transmitting device and a method for transmitting by using a wireless packet including a preamble signal.
2. Description of the Related Art
The Institute of Electrical and Electronics Engineers (IEEE) is now defining a wireless LAN standard called IEEE 802.11n, which aims to achieve a high throughput of 100 Mbps or more. It is very possible that IEEE 802.11n will employ a technique, called multi-input multi-output (MIMO), for using a plurality of antennas in a transmitter and receiver. IEEE 802.11n is required to coexist with the standard IEEE 802.11a where OFDM (Orthogonal Frequency Division Multiplex) is used. So, it is required that IEEE 802.11n wireless transmitting device and receiving device have so called backwards compatibility.
A proposal presented by Jan Boer et al. in “Backwards Compatibility”, IEEE 802.11-03/714r0, introduces a preamble of wireless packet for MIMO. In this proposal, a short-preamble sequence used for time synchronization, frequency synchronization and automatic gain control (AGC), a long-preamble sequence used to estimate a channel impulse response, a signal field indicating a modulation scheme used in the wireless packet, and another signal field for IEEE 802.11n are firstly transmitted from a single particular transmit antenna. Subsequently, long-preamble sequences are transmitted from the other three transmit antennas. After finishing the transmission of the preamble, transmission data is transmitted from all the antennas.
From the short-preamble to the first signal field, the proposed preamble is identical to the preamble stipulated in IEEE 802.11a where single transmit antenna is assumed. Therefore, when wireless receiving devices that conform to IEEE 802.11a receive a wireless packet containing the Boer's proposed preamble, they recognize that the packet is based on IEEE 802.11a. Thus, the proposed preamble conforming to both IEEE 802.11a and IEEE 802.11n enables IEEE 802.11a and IEEE 802.11n to coexist.
Generally, a wireless transmitting device uses a power amplifier for amplifying a transmission signal. Right after the power amplifier is powered on, it generates distortions in an output signal. The power amplifier needs a certain extent of time until the output signal achieve a specified level after it is powered on. A long-preamble sequence included in the wireless packet so as to estimate a channel response is extremely degrades receiving performance of the wireless transmitting device if the long-preamble sequence is not received in a low distortion state. Therefore, it is required to transmit the long-preamble sequence so as to avoid the distortion thereof as much as possible, however, Jan Boer, et al., have not disclosed any measures therefore.